Lubricant providing improved fatigue life

ABSTRACT

The fatigue life of a lubricant composition, particularly one designed for the lubrication of bearings having rolling elements, is markedly improved by incorporating therein a condensation polymer of an alkyl trialkoxy silane or of an alkoxyalkyl trialkoxy silane.

0 United States Patent [1 1 [111 3,816,313 Szieleit June 11, 1974 [54] LUBRICANT PROVIDING IMPROVED 2,897,222 7/1959 Bailey 252/496 x 2,947,772 8/1960 Eynon et a] 252/496 X FATIGUE LIFE 2,995,591 8/196] Kovacich ct a]. 252/496 X [75] Inventor: Hans J. Szieleit, Sarma. ta 3,098,825 7/1963 Shiffter 252/496 x Canada [73] Assignee: Esso Research and Engineering primary w Cannon Compa y, Linden, NJ. Assistant Examiner-W. Cannon [22] Filed: Nov. 17, 1972 [21] App]. No.: 307,492

[57] ABSTRACT :J-S-(gl. The f ig f a l bri nt omposition particud 2 8 R larly one designed for the lubrication of bearings hav- 1 0 an ing rolling elements, is markedly improved by incorporating therein a condensation polymer of an alkyl [56] References Clad trialkoxy silane or of an alkoxyalkyl trialkoxy silane.

UNITED STATES PATENTS 2,780,636 2/1957 Wright et al 252/49.6 X 9 Claims, N0 Drawings LUBRICANT PROVIDING IMPROVED FATIGUE LIFE.

BACKGROUND OF THE INVENTION There has been a need for a lubricant that will prolong the life of bearings by reducing the tendency of metal bearing components to fail as a result of fatigue caused by repeatedstress. This is particularly a problem in rolling contact bearings. See for example Some Effects of Additives on Rolling Contact Fatigue by Fred G. Rounds, ASLE Transactions, Volume 10, pages 243255 (1967).

REFERENCES TO THE PRIOR ART It is known to use alkoxysilanes as hydraulic fluids and lubricants. See for example US. Pat. Nos. 2,947,772, 2,985,678 and 2,995,590. The use of homopolymers of vinylalkoxysilanes, polymerized through the vinyl groups, as foam suppressors in concentrations of from 2 to 50 parts per million in hydrocarbon oils is taught in US. Pat. No. 2,862,885. No prior art is known on the use of condensation polymers of alkoxysilanes as additives capable of increasing the fatigue life of a lubricant composition.

DESCRIPTION OF THE INVENTION In accordance with the present invention it has been found that exceptional antifatigue qualities are imparted to a hydrocarbon lubricant by incorporating therein from about 0.01 to about weight percent of the condensation polymer of an alkyl trialkoxy silane or of an alkoxyalkyl trialkoxy silane. The monomer from which the condensation polymer is derived can be represented by the formula:

wherein R is C, to C2 alkyl or C to C alkoxyalkyl, preferably C to C alkyl or alkoxyalkyl, and R is C, to C alkyl or C to C alkoxyalkyl, preferably C to C alkyl or alkoxyalkyl. By alkoxyalkyl is meant an ether group that can be represented by C O C wherein the sum of n plus m is 2 to 24 in the case of R and 2 to l2 in the case of R. Representative monomers include dodecyl tributoxy silane, decyl tripropoxy silane, ethoxy propyl triheptoxy silane, octadecyl tripentoxy silane, methoxyamyl trihexoxy silane, hexyl tridecoxyl silane, and octyl tri(methoxypropyl oxy) silane. One method for preparing alkyl trialkoxy silanes is to react one mole of'a commercially available alkyl trichloro silane with 3 moles of an aliphatic alcohol. See for example US. Pat. Nos. 2,947,772 and 2,995,590.

The additives of the present invention are condensation polymers of the above-noted alkoxy silanes and can be represented by the formula:

(51A I'M.

wherein x is from about 1 to about 60, or more usually from about 1 to about 40. Usually the additive will comprise a mixture of condensation polymers so that x will represent an average which will usually not be a whole number. The average molecular weights of these additives will be within the range of about 300 to about 30,000. More generally additives with average molecular weight ranging from about 500 to 10,000 will be used.

A condensation polymer can be obtained by refluxing an alkyl trialkoxy silane with water in the presence of a strong acid catalyst which is preferably HCl because of its ease of removal from the reaction mixture. The extent of condensation will depend somewhat on the proportion of water to alkoxy silane; thus in theory one mole of water and two moles of alkoxy silane should give principally the dimer in accordance with the equation:

tions of water.

The condensation polymers can also be formed directly by reaction of an appropriate sodium alcoholate with an appropriate halogenated silane. Thus one mole of octadecyl trichlorosilane will react with 3 moles of sodium pentoxide at ambient temperature to give a condensation polymer of octadecyl tripentoxy silane with sodium chloride as a by-product. Similarly one mole of 3-chloropropyl trichlorosilane will react with 4 moles of sodium pentoxide to give a condensation polymer of pentoxypropyl tripentoxy silane.

The alkoxy silane condensation polymers employed in the present invention will be used in lubricant compositions in amounts ranging from about 0.01 to about 5 percent by weight based on the total composition.

Preferably they will be used within the range of from about 0.1 to about 2 percent by weight. The lubricating oils to which the additives can be added include not only mineral lubricating oils but synthetic oils also. The mineral lubricating oils can be of any preferred type, including those derived from the ordinary paraffinic, naphthenic, asphaltic, or mixed base mineral crude oils by suitable refining methods. The synthetic lubricating oils include not only hydrocarbon oils but also ester oils such as di-2-ethylhexyl sebacate, polyglycols, polycarbonates, glycol esters such as C oxo acid diesters of tetraethylene glycol, and complex esters such as the complex ester formed by reacting one mole of sebacic acid with 2 moles of tetraethylene glycol and 2 moles of 2-ethylhexanoic acid.

In the lubricant compositions, other conventional additives may also be present, including dyes, pour point depressants, antiwear agents, e.g., tricresyl phosphate, zinc dialkyl dithiophosphates of 3 to 8 carbon atoms, antioxidants such as phenylalpha-naphthylamine, tert. octylpheno] sulfide, bisphenols such as 4,4'-methylene bis(2,6-di tert. butylphenol), viscosity index improvers EXAMPLE 1 Preparation A Polymer of Octadecyl Tri-n-Amoxy Silane To a mixture of 1/ 10 mol sodium n-amoxide in 2/10 mol of amyl alcohol and approximately 10 ml of petroleum ether, l/30 mol of octadecyl trichloro silane was added dropwise under stirring at room temperature over a period of about 20 minutes. The product, octadecyl tri-n-amoxy silane, was separated from the byproduct, sodium chloride, by three successive extractions with 10 ml each of petroleum ether. The petroleum ether solvent was then distilled off. The mixture of sodium n-amoxide in amyl alcohol used in this preparation was prepared by adding 1/10 mol of sodium methoxide as a 10/1 solution in methanol to 3/ 10 mol of amyl alcohol.

In separate preparations of the condensation polymer following the above procedure the average molecular weights varied from about 1,000 to about-3,100.

Preparation B Condensation Polymer of iso-Amoxy Propyl Tri iso-Amoxy Silane To a mixture of 0.56 mol of sodium iso-amoxide, 0.5 mol isoamylalcohol and 300 ml petroleum ether, 0.175 mol of 3-chloropropyl trichlorosilane was added dropwise under stirring at room temperature, over a period of about 20-25 minutes. The resulting product was extracted with petroleum ether as in Preparation A, and the petroleum ether solvent was then distilled off.

The average molecular weights of condensation polymers prepared by the above procedure ranged from about 560 to about 1,440 if care was taken to dry the reactants. Without such care the molecular weight was found to be considerably higher.

Preparation C Condensation Polymer of Ethoxypropyl Tri-iso-Amoxy Silane A 1/10 mol quantity (19.9 g) of 3-chloropropyl trimethoxy silane was added dropwise with stirring at room temperature to 1/ 10 mol of sodium ethoxide as a 10/1 solution in ethanol. To complete the reaction, the mixture was refluxed for 2 hours and the sediment (NaCl) removed by filtration. The excess ethanol was distilled off under vacuum. 40 g (0.45 mol) of iso-amyl alcohol and two drops of a compound which released hydrogen chloride (chloro methyl trimethyl silane) were added and the mixture refluxed for 2 hours. The liberated methanol and the excess iso-amyl alcohol were distilled off. The molecular weight of the resulting product was 828 i 10 percent, indicating the probable formation of the trimer.

Preparation D Condensation Polymerization of Ethoxypropyl Tri iso-Amoxy Silane (ETAS) A mixture of 1.5 ml of 10 percent aqueous HCl and 20 g ETAS (MW2828) was refluxed for 2 hours. The liberated iso-amyl alcohol was distilled off under vacuum (ca 1 to 2 mm Hg). The yield was 11.4 g of the condensed version of ETAS having an average molecular weight of 3,510 i 10 percent. This would correspond to approximately 15.5 units of per molecule.

Preparation E Condensation Polymer of Methoxypropyl Tri-iso-Octoxy Silane The procedure of Preparation C was followed, but employing sodium methoxide in place of sodium ethoxide and iso-octyl alcohol in place of iso-amyl alcohol. No determination of the molecular weight of the condensation polymer was made.

EXAMPLE 2 Lubricating oil blends were prepared using either a base oil X, which was an SAE 10 grade, phenol extracted, dewaxed and hydrofined lube distillate from a Western Canadian crude oil, or a base oil Y, which vwas a refined SAE 10 grade multipurpose hydraulic oil containing a pour point depressant (0.7 vol. percent of a mixture of wax-alkylated naphthalene and methacrylate ester concentrate) an oxidation inhibitor (0.3 wt. percent 2,6-ditert. butyl p-cresol) an antiwear agent (0.5 vol. percent of dihydrocarbyl dithio-phosphate) and a rust inhibitor (0.05 vol. percent of a 50 percent oil concentrate of neutral barium dinonyl naphthalene sulfonate plus 0.04 vol. percent of ethylene oxide treated tetrapropenyl succinic acid). The blends were prepared by adding, by simple mixing, various concentrations of condensation polymers of alkoxy silanes prepared by the procedures described above. Various concentrations and molecular weights were used in the different blends. Each of the blends as well as each of the base oils was subjected to a test designed to determine the effect of the oils on the fatigue life of bearings. This test is known to correlate with actual field results. The test machine used was a rolling four-ball machine in which three steel balls are allowed to roll freely in a conforming race, while a fourth steel ball which is held firmly in a chuck is pressed on the top of the other three balls and rotated under load. The speed of rotation was 1,600 rpm and the applied load was 887 pounds, which corresponds to an initial maximum contact stress of 1.07 X 10 psi. To run the test the required amount of test oil was poured into the reservoir and the equipment was brought up to the test temperature of F. Each test was run until one of the balls developed a fatigue spall. The excessive vibrations that resulted from the failure of one of the balls actuated a vibration switch which automatically turned off the machine. The longer the time period to failure the greater are the antifatigue properties of the oil being tested. The results obtained, in terms of millions of revolutions until failure, are shown in Table l which follows:

TABLE I Average Mean Fatigue Weight Mol. Wt. Life Oil Tested Additive of Additive X Rev.

Base Oil X 0.44 Oil X B 0.15 8000 1.58 Base Oil Y 1.] Oil Y A 0.5 l0l0 2.2 0.5 3100 2.7 Oil Y B 0.05 8000 1.3 0.10 8000 2.0 0.15 8000 3.3 0.20 8000 3.8 Oil Y C 0.5 828 2.4 Oil Y D 0.1 3510 2.7 Oil Y E 0.3 2.2

It will be noted that in each instance the mean fatigue life of the lubricating oil was increased by the addition of an alkoxy silane condensation polymer. The data show that at a given concentration of additive an in crease in molecular weight effects an improvement in anti-fatigue properties and that with. an additive of a given molecular weight, fatigue life increases with increased concentration of the additive in the compositron.

EXAMPLE 3 Using a conventional procedure, a lubricating grease is prepared from 76 parts of weight of 12- hydroxystearic acid, ll.5 parts of lithium hydroxide monohydrate, and 908 parts of a solvent-refined mineral lubricating oil of about 460 SUS viscosity measured at 100 F. To prepare the grease, the 12- hydroxystearic acid is added to about half of the total oil used in the complete grease, the mixture is heated to about l90200 F., the lithium hydroxide is added in the form of an aqueous solution, and the resulting mixture is then heated with stirring to a final temperature of about 380390 F.-Then the remaining portion of the base oil is stirred in and the mixture is cooled to ambient temperature. When cooling has reached about 100 F. during cooling, 5 parts of 1,010 molecular weight condensation polymer of octadecyl tri-n-amoxy silane (Preparation A of Example 1) is added and the grease is milled in a conventional grease mill.

It will be understood that there is no intention that the scope of this invention be limited to the foregoing specific examples which have been presented merely as illustrative of the invention.

What is claimed is:

l. A lubricating oil composition comprising a major proportion of a hydrocarbon lubricating oil to which has been added from about 0.0l to about 5 percent by weight of the condensation polymer of an alkyl or alkoxy alkyl trialkoxy silane, said condensation polymer being represented by the formula:

5R it.

wherein X is from about l to about 60, R is C to C alkyl, or alkoxy alkyl totaling 2 to 24 carbon atoms, and R is C to C alkyl, or alkoxy alkyl totaling 2 to 12 carbon atoms.

2. Composition as defined by claim 1 wherein X is from about 1 to about 40.

3. Composition as defined by claim 1 wherein said condensation polymer has an average molecular weight of from about 300 to about 30,000.

4. Composition as defined by claim 1 wherein said condensation polymer is that of octadecyl tri-n-amoxy silane.

5. Composition as defined by claim 1 wherein said condensation polymer is that of isoamoxypropyl triisoamoxy silane. I

6. Composition as defined by claim 1 wherein said condensation polymer is that of methoxypropyl trioctoxy silane.

7. Composition as defined by claim 1 wherein said condensation polymer is that of ethoxypropyl triisoamoxy silane.

8. Composition as defined by claim 1 which additionally contains a grease thickener.

9. Composition as defined by claim 1 which additionally contains at least one additive selected from the group consisting of an antioxidant, a rust inhibitor and an antiwear additive. 

2. Composition as defined by claim 1 wherein X is from about 1 to about
 40. 3. Composition as defined by claim 1 wherein said condensation polymer has an average molecular weight of from about 300 to about 30,000.
 4. Composition as defined by claim 1 wherein said condensation polymer is that of octadecyl tri-n-amoxy silane.
 5. Composition as defined by claim 1 wherein said condensation polymer is that of isoamoxypropyl tri-isoamoxy silane.
 6. Composition as defined by claim 1 wherein said condensation polymer is that of methoxypropyl tri-octoxy silane.
 7. Composition as defined by claim 1 wherein said condensation polymer is that of ethoxypropyl tri-isoamoxy silane.
 8. Composition as defined by claim 1 which additionally contains a grease thickener.
 9. Composition as defined by claim 1 which additionally contains at least one additive selected from the group consisting of an antioxidant, a rust inhibitor and an antiwear additive. 